1. Field of the Invention
The present invention relates to a magnetron sputtering apparatus. More particularly, the present invention relates to a magnetron sputtering apparatus employing a mask intimately affixed to a film-forming surface.
2. Background of the Invention
Optical discs, such as so-called Compact Discs (CDs), have come into widespread use for recording digital audio informations or video informations. Such optical disc has a substrate of a transparent synthetic resin, such as polycarbonate, on the surface of which a thin film layer of aluminum (Al) of high reflectivity is formed by vapor deposition or sputtering. On the surface of the substrate carrying the Al thin film layer is formed a pattern of micro-sized lands and recesses, termed pits, corresponding to the digital information of "1" or "0". The light beam is radiated on these pits through the substrate and the information recorded on the optical disc is read on the basis of the reflected light beam from the thin film layer.
Since a thin film can be formed on an optical disc substrate within a shorter time, an apparatus shown in FIG. 1 is employed for continuously sputtering plural discs one by one.
FIG. 1 shows only the essential mechanism of such magnetron sputtering apparatus. In FIG. 1, substrates 102, 102, . . . of optical discs, such as CDs, are transported in succession by an external transporting mechanism 101, such as a belt conveyor. The substrates 102, 102 thus transported are sucked by a suction pad 104 of a disk-shaped transporting device 103, rotatable about its axis and movable between an upward direction and a downward direction, and are transported in this state into a sputtering chamber 105.
The substrate 102, transported by the suction pad 104, is set in the sputtering chamber 105 on a transporting table 106 which is similarly rotatable about its axis and movable in the upward direction and the down ward direction. The substrate 102, set on the transporting table 106, is transported to a position facing a sputtering source 107 by the rotation and vertical movement of the transporting table 106. Film spatter is carried out by the sputtering source 107 on the substrate 102 mounted opposing the sputtering source 107. Following the film sputter, the substrate 102 is again set on the transporting table 106 and taken out to outside by the transporting device 103.
The substrate 102, transported into the sputtering chamber 105, is moved in the upward direction by the transporting table 106 into intimate contact with the lower end face of a mask 108 provided within the sputtering source 107, as shown to an enlarged scale in FIG. 2. A film-forming chamber 109, in which the film sputter is carried out by sputtering, includes anti-sputter shields 112a, 112b and the mask 108 mounted on the inner wall surface of an outer enclosure 110. If there is no substrate 102 in the film-forming chamber 109, the inside of the film-forming chamber 109 is evacuated via a space 111 in the mask 108 by a vacuum pump, not shown.
The substrate 102, transported by the transporting table 106, is supported by the mask 108, and yet has its non-film-forming portion shielded by the mask 108. The mask 108 is fabricated to high precision and intimately bonded and secured to the outer enclosure 110 by utilizing its force of thermal expansion. An Al target 113 is secured to a target cooling plate 114 for constituting a cathode electrode and supplies a magnetic field in the film-forming chamber 109 in cooperation with a magnet 115. The magnet 115 is mounted for being rotated at a position offset from the center of the film-forming chamber 109 and is adapted for supplying a more uniform magnetic field for improving the exploitation efficiency of the target 113.
The cathode electrode induces a discharge electrical field on the order of 75 (W/cm.sup.2) on the target surface. In order to suppress the temperature on the target 113 during film formation to not higher than 200 to 300 (.degree. C.), a ring-shaped hollow space is formed within the inside of the target cooling plate 114 so as to be supplied with the cooling water via a water supply pipe 116. The inside of the film-forming chamber 109 is supplied an argon gas required fir film sputter through a gas inlet tube 117. The pressure during film formation is in a range of 0.2 to 5.0 (Pa). Since the magnetron sputtering apparatus is used under different operating conditions from one user to another, the internal pressure is known to be varied over an extensive range as described above.
With the above-described magnetron sputtering apparatus, the Al target 113 is struck by argon gas atoms to produce a sputtering action to form an Al film on the surface of the substrate 102. After the film sputter, ejection of argon gas atoms ceases, and the substrate 102 is again placed on the transporting table 106 so as to be taken out by the transporting device 103.
With the above-described magnetron sputtering apparatus, a film sputtered on the substrates 102, 102 . . . transported thereto in succession occurs at a short cycle of about 6 seconds per substrate. Consequently, the time necessary for actual film formation is an extremely short period on the order of two seconds during which the electrical field is supplied to the Al target 113.
It is however not possible with the mask 108 now in use to form a film on all surface of the substrate 102, as shown in FIGS. 3 and 4. The reason is that four pillars 120 are provided for interconnecting a central mask portion 118 for masking the central portion of the substrate 102 and an outer peripheral mask portion 119 for masking the outer peripheral portion of the substrate, as shown in FIGS. 3 and 4. That is, since these pillars 120 are provided on the surface of the substrate 102 to be sputtered, atoms or molecules struck out of the target 113 are screened by these pillars 120, as a result of which the thin film is not formed on the all surface of the substrate.